Organic matter makes up only a small fraction of the total materials in soil, yet it is extremely important. This organic material is made up of living organisms such as plants and animals, dead plants and animals, and nutrients that have come from decomposed plants and animals.

The amount of life present in the soil is surprisingly large. Take, for example, just a small handful of dirt that you might pick up outside in your backyard. In your hand you likely hold several hundred trillion different microscopic lifeforms. Now consider your entire back yard. Within that small portion of the Earth’s soil are likely hundreds and hundreds of trillions of lifeforms, including over 100,000 earth worms, in a typical sized yard.